CBO Director Keith Hall outlined the projections in a Wednesday letter to House Ways and Means Committee ranking member Rep. Richard Neal, D-Mass. They are partly based on calculations by the Joint Committee on Taxation.
The deficit figure does not include the estimated effects of economic growth. Republicans argue that growth sparked by the bill will help to offset, or cancel out entirely, the budget shortfall caused by broad tax cuts.
Under budget rules congressional Republicans are using to pass a tax plan, the bill can only increase deficits by $1.5 trillion over 10 years, before growth is taken into account.
The plan, called the Tax Cuts and Jobs Act, cuts the corporate tax rate from 35 percent to 20 percent, while moderately reducing household income-tax rates. It changes some popular provisions such as the mortgage interest deduction, but leaves others, like the 401(k) tax benefit, unchanged.
The House hopes to pass its bill as early as next week. The Senate plans to release its own proposal, which likely will contain differences from the House bill.
Lawmakers are looking for ways to gain revenue to help offset the tax cuts. One possible provision to save money is repealing the Affordable Care Act rule that requires Americans to have health insurance or pay a penalty.
House Republicans may be reluctant to scrap the rule because doing so could run into resistance in the Senate.
A separate report from Fitch Ratings on Tuesday estimated that the GOP tax cuts would not pay for themselves and instead would add "significantly" to U.S. debt.